1. Field of the Invention
The present invention relates to an ignition control system for an internal combustion engine mounted in, for example, a motor vehicle, and more particularly, to an ignition device of an ignition control system for an internal combustion engine which causes a current to be conducted through and shut off from a primary coil of an ignition coil by means of a switching element to generate a high voltage for ignition in a secondary coil of the ignition coil.
2. Description of the Related Art
In a conventional ignition control system for an internal combustion engine, an ignition device having a coil is provided with a dedicated terminal for outputting a failure diagnosis signal obtained by monitoring an ignition operation, so the failure diagnosis signal is output to an electronic control circuit side through a path different from a path for an ignition signal terminal (e.g., see JP 64-35078 A).
In the above-mentioned structure, however, the necessity for the dedicated terminal for outputting the failure diagnosis signal causes problems such as an increase in the number of parts of an ignition device and an increase in the number of harnesses between the ignition device and the electronic control circuit.
In order to solve those problems, another ignition device for an internal combustion engine is equipped with an electronic control circuit for outputting an ignition signal for controlling an ignition timing, an igniter driven based on the ignition signal from the electronic control circuit, and a failure detecting circuit for detecting a failure signal obtained from a current flowing through a secondary coil of an ignition coil in the igniter and returning the failure signal to the electronic control circuit, and is structured such that the same signal wire is used for the ignition signal and the failure signal. In the aforementioned ignition device for the internal combustion engine, with a view to preventing the ignition signal and the failure signal from being output simultaneously, the ignition signal is kept from being turned ON inside the igniter when the failure signal is output (e.g., see JP 08-128381 A).
In this kind of ignition control system for an internal combustion engine, a failure diagnosis is often carried out from an ion current obtained from a secondary coil of an ignition coil after ignition and explosion. In a device having this construction as well, similar problems such as an increase in the number of parts of the device and an increase in the number of harnesses are caused when the device is provided with a dedicated terminal for outputting a failure diagnosis signal.
Furthermore, in a device for outputting an ion current as a failure diagnosis signal, a leak current flows when soot or the like is generated between electrodes due to the smoldering of an ignition plug, so there is caused a state in which the ion current flows constantly in a fictitious manner. In consequence, the ion current is output even at a timing when an ignition signal is to be supplied, so there is a problem in that the ignition signal cannot be transmitted accurately to a circuit at a subsequent stage.